1. Field of the Invention
The present invention relates to a vacuum cleaner for industrial or household use.
2. Description of Related Art
A conventional vacuum cleaner of the upright type is disclosed in, for instance, West German Patent Auslegeschrift DE 3431164C2. The disclosed vacuum cleaner is a cylinder-type vacuum cleaner such as that shown in FIG. 6, in which an infrared sensor is employed though its specific construction is not described in detail.
In the case of an upright vacuum cleaner, the dust collected by the cleaner brings forth the condition shown in FIGS. 7 and 8. When a certain amount of dust has been collected in a paper bag 25 fixed to an end portion of an intake section 11 projecting into a dust. collecting section 8, it becomes difficult to send air from the intake section 11 into the paper bag 25 so as to flow through the bag 25. On the other hand, the rotation of an electric blower 9 at a certain number of revolutions per unit time causes the air within the dust collecting section 8 to be sent to the outside. Therefore, when the amount of the dust collected increases to a certain amount, the internal pressure within the dust collecting section 8 drops, and the pressure within a passage 35, defined by a member fixed to a position of the section 8 by screws, also drops. A movable member 37 remains motionless while being held in place by a spring 36 disposed in the passage 35 when the internal pressure is above a certain level. However, when the internal pressure becomes lower than this level, the movable member 37 moves compressing the spring 36, so as to allow an inflow of air (indicated by the arrows in FIG. 8) from the outside of the section 8 to the inside thereof. This inflow of air prevents generation of a vacuum within the body of the cleaner, thereby preventing overheating of members such as the motor for the blower, and the resultant deformation of the resin materials used in the cleaner. The movement of the movable member 37 allows the user to be informed of whether the paper bag 25 is filled with dust or not.
A different arrangement is disclosed in DE 3431164C2, in which, as shown in FIG. 6, a detecting means 30 is provided in a handle 17 between a flexible hose 31 extending from a cleaner body 34 and a rigid pipe 32 provided with a suction brush 33 at one end thereof. This is an arrangement applicable to a cylinder-type vacuum cleaner.
Recently, the above-described arrangement of the upright vacuum cleaner has experienced a problem arising from the increase of fibrous dust, such as lint, resulting from changes in the living or working environment. Fibrous dust is, when received in the paper bag 25, bulkier than such dust as earth and sand. Even when fibrous dust fills the paper bag 25 and it has indeed caused a drop in the internal pressure within the dust collecting section 8, the internal pressure does not easily become low enough to cause the movement of the movable member 37. This is because the fibrous dust filling the bag 25 has a lot of voids or vacancies between its specks of dust. If the cleaner in this condition is continuously used, dust will be accumulated in the intake section 11 or in a hose 10. In the end, the vacuum cleaner will not be able to suck dust any more. What is worse is that the dust-filled condition of the cleaner may not be found out until the bag 25 is removed.
Some vacuum cleaners have a sensor employing a light-emitting element and a light-receiving element. These elements are usually protected by a transparent protective cover. However, when substances such as dry sand or earth, or moist fiber, earth or sand have adhered to the cover, the light used in the sensor is blocked by the adhering substance, thereby deteriorating the sensitivity of the sensor. In order to avoid this problem, it is necessary that the sensor is cleaned frequently by, for instance, wiping it with a piece of cloth or the like. However, with the conventional vacuum cleaners, it is impossible to clean the sensor positively and easily because only one side of the sensor can be wiped and because the way the sensor is contaminated cannot exactly be known.